The present invention relates to a method of manufacturing an oxide dispersion strengthened (ODS) martensitic steel excellent in high-temperature strength.
The oxide dispersion strengthened martensitic steel of the present invention can be advantageously used as a fuel cladding tube material of a fast breeder reactor, a first wall material of a nuclear fusion reactor, a material for thermal power generation, etc. in which excellent high-temperature strength and creep strength are required.
Although austenitic stainless steels have hitherto been used in the component members of nuclear reactors, especially fast reactors which are required to have excellent high-temperature strength and resistance to neutron irradiation, they have limitations on irradiation resistance such as swelling resistance. On the other hand, martensitic stainless steels have the disadvantage of low high-temperature strength although they are excellent in irradiation resistance.
Therefore, oxide dispersion strengthened martensitic steels have been developed as materials that combined irradiation resistance and high-temperature strength, and there have been proposed techniques for improving high-temperature strength by adding Ti to oxide dispersion strengthened martensitic steels, thereby finely dispersing oxide particles.
For example, Japanese Patent Publication No. 5-18897/1993 discloses a tempered oxide dispersion strengthened martensitic steel which comprises, as expressed by % by weight, 0.05 to 0.25% C, not more than 0.1% Si, not more than 0.1% Mn, 8 to 12% Cr (12% being excluded), 0.1 to 4.0% in total of Mo+W, not more than 0.01% O (O in Y2O3 and TiO2 being excluded) with the balance being Fe and unavoidable impurities, and in which complex oxide particles comprising Y2O3 and TiO2 having an average particle diameter of not more than 1,000 angstroms are homogeneously dispersed in the matrix in an amount of 0.1 to 1.0% in total of Y2O3+TiO2 and in the range of 0.5 to 2.0 of the molecular ratio TiO2/Y2O3.
However, even when oxide dispersion strengthened martensitic steels are produced by adjusting the total amount of Y2O3 and TiO2 and the ratio of these oxides as disclosed in Japanese Patent Publication No. 5-18897/1993, there are cases where oxide particles are not finely dispersed in a homogeneous manner and it follows that in such cases the expected effect on an improvement in high-temperature strength cannot be achieved.